1. Field of the Invention
The present invention relates generally to methods for the fabrication of composite materials. More particularly, the present invention relates to a method for forming reinforced refractory composite tubing having very high fiber volume and very low porosity.
Reinforced composite tubing is useful for a number of purposes, such as the construction of structural frameworks. Desirably, such structural tubing will possess high tensile and compression strength, even at high and low temperature extremes as well as high specific strength and modulus.
Heretofore, refractory composite tubing, e.g., ceramic and graphite matrix tubing, has usually been made from braided reinforcement fabrics or by using an involute lay-up process. Although suitable for many purposes, braided composite tubing generally has a reduced fiber volume in the primary load direction which can reduce its usefulness. The refractory composite tubing made by involute rolling techniques generally possesses higher strength (improved fiber orientation can be achieved), but is relatively difficult to fabricate. In one such technique, a series of narrow strips of reinforcement fabric are layered over one another in an overlapping fashion. Pressure may be applied to the layers during curing, and intermediate bleeder cloths are frequently necessary to allow the escape of entrapped air. Refractory composite tubing prepared by such an involute technique is subject to separation of the layers when exposed to extreme temperature variations. Both braided and involute tubing suffer from substantial dimensional deviations so that product having reproducible dimension is difficult to achieve.
It would therefore be desirable to provide methods for fabricating reinforced refractory composite tubing having high fiber volume and low porosity which allow for selectable strength characteristics with optimized fiber volume and fiber orientation. Such methods should also provide tubing which is substantially free from wrinkling and other mechanical defects and which possesses highly accurate and reproducible dimensions and does not necessarily require the use of bleeder cloth during fabrication. The resulting tubing should be able to withstand severe temperature variations and temperature cycling without unbonding of the reinforcement layers or filaments from the matrix.
2. Description of the Background Art
Composite flexible tubing suitable for fishing rods and other light duty uses have been made from non-refractory fabric prepregs using rolling plate and shear-type wrappers available from commercial suppliers, such as Century Designs, Inc., San Diego, California. Three-bar wrappers of the type which may be employed in the present invention have been used to produce non-refractory composites (e.g., glass fiber reinforced plastics) for uses such as boat masts and pole vault poles. Vacuum bag curing of non-refractory composite articles is known.